The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume, and to access this information more efficiently. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To accomplish efficient extraction and distribution of such a large volume of information, the use of storage disks onto which a large volume of information is able to be input and output at high speed is appropriate. An inherent problem in the use of magnetic disks for this purpose is that, accompanying recording density increases, thermal fluctuations cause a decrease in a recorded signal level. This is because a magnetic recording medium constitutes an agglomerate of magnetized fine crystals, wherein thermal fluctuations cause a reduction in the volume of these fine crystals. To produce what is regarded as a sufficient thermal fluctuation-resistance stability, it is thought that the value of the oft-employed thermal fluctuation index Kβ (where Kβ=KuV/kT, with Ku being magnetic anisotropy, V being particle volume, T being absolute temperature, and k being the Boltzmann factor) should be not less than about 70. Assuming a fixed Ku and T (based on material used and operating environment), the smaller the particle volume V becomes, the more likely it is that magnetization reversal due to thermal fluctuation will occur. In the absence of a reduction in the particle volume V accompanying an increase in the recording density increase and a decrease in the volume of recording film occupied by a single bit, thermal fluctuations become significant. When magnetic anisotropy Ku is increased for the purpose of suppressing these fluctuations, the magnetic field of the magnetization reversal required for magnetic recording exceeds the recording magnetic field that is able to be generated by the recording head (and specifically the write element), and recording is rendered impossible.
Several attempts have been made to overcome these deficiencies. In one such attempt, as described in U.S. Patent Application Publication No. US 2008/0019040, a MAMR technique is described. As shown in FIG. 1, recording using this MAMR technique involves the application of not only a write magnetic field 301 (Hw) from a perpendicular main pole 305 of a magnetic recording head 300, but also the application of a high-frequency assistance microwave magnetic field 302 (Hhf) from a magnetic field generating layer (FGL) 303 of a spin torque oscillator (STO) 308 arranged adjacent to the main pole 305 onto a magnetic recording medium 307 having large magnetic anisotropy that, as a result, establishes the target recording region as a magnetic resonance state and, in turn, induces magnetization and reduces the magnetic field for magnetization reversal. Furthermore, a gap magnetic field 309 (Hgap) is produced between the main pole 305 and the opposite pole or trailing shield 306.
This allows for recording to be performed in the microwave irradiated range of the magnetic recording medium 307 which corresponds to a high recording density in excess of about 1 Tbit/in2 at which, in a conventional magnetic head, recording had proved problematic due to the inadequate recording magnetic field. However, the inherent magnetization reversal of the pinned layer 304 in the STO 308 is both problematic and time-consuming and, accordingly, the high-speed information transfer write efficiency of this apparatus is poor.
Japanese Patent No. 5172004 discloses a method in which a two-layer FGL is employed as a high-frequency magnetic field source. The FGL does not comprise a pinned layer, but instead rotates (in an antiparallel direction) while maintaining the antiparallel magnetization relationship of the layers. However, this structure also has problems associated with it in regard to reversal speed. Accordingly, it would be beneficial to have a MAMR head which is capable of fast high-density magnetic recording.